1. Field of the Invention
An object of the present invention is an optical coupler. An optical coupler of this kind is used to transmit an optical signal between a first device on the one hand and at least two second devices on the other. For example, an optical coupler links a sender device or sender unit sending an optical signal to two receivers of this optical signal. It can be used more particularly in the monitoring of control devices, especially those positioned in locomotives. Such couplers provide redundancy and even multiple back-up for surveillance systems. This coupler implements two optical fibers and has the advantage of transmitting the signal with almost no loss and without disturbance since it is not subject to electromagnetic disturbance. Indeed, with a coupler according to the invention, the losses between the signal sent and the signal received amount to less than 3 decibels.
2. Description of the Prior Art
In the prior art, there is a known optical coupler used, for example, to connect a sender unit to two receivers. On the sender unit side, this coupler has a first optical fiber having a first end that faces an optical source. Since the second end of this first optical fiber cannot be presented directly so that it faces two different receivers, the coupler can be used to connect the first fiber to two other fibers, each positioned so as to face a different receiver in order to transmit the sent signal to each of these receivers.
Generally, a coupler is centralized by joining the two fibers together so that the light can pass from the sender unit to the two receivers, or else it can be made by juxtaposing the two “receiver” fibers which will then be aligned and positioned so as to be facing the “sender” fiber. In order that the signal conveyed in the first “sender” optical fiber may be satisfactorily transmitted to the two “receiver” optical fibers, each of these “receiver” optical fibers should be presented so as to face the beam sent out by the “sender” fiber. To this end, since an optical fiber is generally surrounded by a sheath and a cable, the ends of the two “sender” optical fibers are generally completely stripped of their sheath so that they can be bonded as closely together as possible. Thus, if the beam given by the optical signal conveyed by the first optical fiber has a certain diameter, it is seen to it that the two second optical fibers are arranged in such a way that they equitably share the position facing the beam.
In general, all the optical fibers of the coupler have a same external diameter with or without sheath, and a same internal diameter. When the two fibers are bared, and attached together, then the distance between the two centers is equal to twice the radius of the fiber.
To reduce the losses between the first optical fiber and the two second optical fibers, there are prior art solutions in which the beam is widened so that it covers the totality of the attached surfaces of the bared ends of the two second optical fibers. In this case, a lens needs to be positioned between the first optical fiber and the two second optical fibers. This assembly is difficult to make and costly. Moreover, it does not completely reduce signal losses.
It is an object of the invention to resolve the problem posed. Indeed, an optical coupler according to the invention very appreciably restricts signal transmission losses. Indeed, the optical coupler of the invention is made in such a way that each of the two optical fibers, each connected to a receiver, as described in the example described here above, has one end positioned so as to be directly facing the beam sent out by the sender device. Reciprocally the invention also enables transmission without signal losses even if each of the two fibers is respectively connected to a sender unit and if each of these two fibers is presented so as to be facing a common receiver.
Indeed, with a coupler according to the invention, a single sender unit is connected to two different receivers by means of two distinct optical fibers each receiving the same signal sent. The particular feature of the invention is that the two optical fibers are attached to each other on the side where the first device is a single device and this first device sends a signal to be transmitted to the several other devices, or this first device receives signals coming from several other devices.
In preferred embodiments, the manner of attaching the two optical fibers gives loss-free transmission and furthermore brings the two optical fibers close to each other to the greatest possible extent so that they are presented in one and the same connector. Indeed, the two optical fibers are partially bared and inserted into a same sleeve.